An update of sorts.
After running every single Apple recommended trouble shooting fix, I’m still in the same boat, but there was a small bright spot.
Originally, I was working over a network, from a Synology NAS. I moved the project & media to my local drive, cleared as much unnecessary data from the computer as possible, restarted, and got one clean export of the project. One.
For the greater good, I attempted more exports after the successful one, but all subsequent efforts failed.
It’s looking like it may be a memory issue. Will update on further research/attempts.